32 BMW 1973 R75/5 Repair Stripped Thread in Handlebar Control

After I got the handlebar assembly castings back from powder coating and put them back together, I discovered a problem with the left side clutch assembly. Referring to the diagram below,

Source: MAX BMW Parts Fiche
http://www.maxbmwmotorcycles.com/fiche/DiagramsMid/B0000664.png?v=08102012

the pinch bolt (5) is supposed to be a 6 mm x 1 socket head cap screw that squeezes the bracket around the handlebar so the serrated perch (16) (see diagram below) grabs the bar keeping the assembly from rotating.

Source: Hucky’s Spare Parts & Repros http://www.bmwhucky.com/007532.html

Instead of the socket head cap screw, there was a smaller diameter hex bolt with a nut to tighten the assembly. On the throttle assembly on the right, there was a 6mm hex bolt so I thought the socket head cap screws had been lost and this was the fix. I bought new socket head cap screws and as I screwed in a new one, it wouldn’t tight up.  Ah, so the threads are stripped and that’s why the small diameter bolt and nut was used.

My first thought was to tap the hole with a 7 mm tap.  The drill diameter for that is 6.1 mm, so that should work.  I posted a note to the Airhead BMW Club and sent an Email to a technical discussion forum for airhead owners with my idea. Tom Cutter replied with “helicoil is  best” and someone else replied that M7 bolts are made from Unobtainium.  So, instead of a $0.65 bolt,  I bought a $40.00 6mm x 1 helicoil kit at my local NAPA store. But on the bright side, now I can repair another 11 stripped 6 mm x 1 threads. When I look at it that way the kit only costs  $3.33 per stripped thread.  🙂

Honestly, in all the years I’ve been tinkering, I never had to do a HeliCoil repair.  But through the magic of YouTube, I saw how to do it on a car engine block, and that’s close enough to a BMW handlebar assembly to make it look pretty easy.

Here’s the NAPA kit I bought.

Helicoil M6x1 Repair Kit

NAPA Helicoil M6x1 Repair Kit

Here is the assembly showing the stripped thread.

Striped Threads & Compression Bolt

Stripped Thread & Compression Bolt

The instructions said to drill out the existing hole with a 1/4 inch drill.  Hmm, nice new powder coated assembly and here I am attacking it with a drill … sigh.

Drill with 1/4 inch Bit

Drill with 1/4 Inch Bit

The drill is variable speed so I started at low speed so when the bit grabbed it wouldn’t fling the assembly across the room.  Carefully working the bit into the threads, I got the hole drilled without damaging the powder coat.

I used the special HeliCoil tap to cut the threads for the insert.

Helicoil Tap

HeliCoil Tap

I put a little tap cutting oil on the tap threads and used a tap handle to cut them.

Ready to Tap

Ready to Tap HeliCoil Threads

The assembly is split so the front side where the bolt head rests doesn’t have any threads and the back side does. So I tapped the hole from the backside.

Threading Heilcoil Tap

Running Tap in from Back Side of Assembly

I went slowly and was careful to keep the tap square to the hole on the first few turns. And, voila, a HeliCoil threaded hole.

Tapped Hole

New HeliCoil Threads

The kit includes a tool for installing a thread insert.  The insert goes inside the tool through a cutout on the side with the tang on the bottom of the insert pointing to the bottom of the tool.

Helicoil Insert and Insert Threading Tool

HeliCoil Insert and Insert Installation Tool

Insert Threading Tool

Insert Loading into Installation Tool

There is a threaded rod inside the Installation tool that screws through the inside of the insert until a little ridge on the end of the threaded rod catches on the tang at the bottom of the insert.

Tang at Bottom of Insert

Threaded Rod with Ridge Engaging Tang on the End of the Insert

The end of the threaded rod is square so it will fit a small tap handle.

Tap Handle on Insert Tool

Insert Installation Tool with Tap Handle

I mounted the assembly in the vice using rubber jaws. As the threaded rod is screwed down, the insert coils are compressed so the coils will engage with the the threads in the hole. There are no threads on the front side of the hole, so I threaded the insert into the backside threads. But the diameter of the Installation tool is large enough that I couldn’t keep it square with the hole. I figured the insert coils would engage with the threads and since the coils are flexible the insert should thread into the hole correctly.

Threading Insert into Tapped Hole

Threading the Insert into Tapped Hole From Backside of Assembly

I used a punch to knock the tang off the end of the insert and then threaded the new socket head cap screw into the HeliCoil and tightened it up enough to see the ends of the slot start to close.  Success.

M6 Bolt Working Again

New M6 Socket Head Screw Works Perfectly

Here are the finished left and right hand handlebar assemblies with new powder coating and polished levers.  I think they are going to look very nice on the new handlebar.

Assembled Left Side Clutch Assembly

Assembled Left Side Clutch Assembly

Assembled Right Side Throttle Assembly

Assembled Right Side Throttle Assembly

7 thoughts on “32 BMW 1973 R75/5 Repair Stripped Thread in Handlebar Control

  1. Pingback: 1973 BMW R75/5: Repairing Stripped Threads in Handlebar Assembly | Motorcycles & Other Musings

  2. Nice fix. I’ve never used helicoils so it’s nice to see how it’s done. Thanks for posting this.

    BTW…M7 bolts, nuts, etc, in various configurations are available at Home Depot, at least at the one I frequent.

    • Hi Mark,

      Cool beans. I figured it may be helpful to show how this is done.

      By the way, there are no 7 mm socket head cap screws listed for Home Depot, but there are a couple of hex head bolts. I also did a Google search on them and found them “not available” even with large bolt distribution companies. I found a number of blogs and forum comments about them not being commonly used.

      The nice part of doing this repair is that the standard 6 mm socket head cap screws are retained and I know one day I’ll thank myself for not having used a “one off” bolt ;-).

      Best.
      Brook.

  3. Dang Brook –

    Every time I think I might have to do a particular job, you’ve already encountered it, figured out the gotchas and documented it all for those who follow. Keep up the great job!

    • Hi Shane,

      Well, that’s good news because I if there is one thing I do well is the same job three times until I figure out the right way to do it 🙂 I’m glad some of the material I’ve posted is helping you out. Remember, there can never be too many Airheads on the road my friend.

      Best.
      Brook.

  4. Those who own things are owned by things… eventually it leads us to helicoils. Fun aren’t they? BTW, M7 bolts might be available from Home Despot, but the fasteners are total crap.

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